This invention relates to an exposure method and a device manufacturing method using the same. More particularly, the invention is concerned with an exposure apparatus or a projection exposure apparatus based on a proximity method, a step-and-repeat method or a step-and-scan method, for use in the production of various devices such as ICs, LSIs, CCDs, liquid crystal panels, or magnetic heads, for example, wherein a fine electronic circuit pattern formed on a reticle (first object) is lithographically transferred to a wafer (second object) after they are relatively aligned.
In projection exposure apparatuses for the manufacture of semiconductor devices, improvement of the precision of relative alignment between a reticle and a wafer is an important factor for enlargement of integration of the semiconductor device. Recently, an alignment precision higher than a submicron order is required to meet further miniaturization of semiconductor chips.
In reduction projection type exposure apparatuses for semiconductor device production, a circuit pattern of a reticle (first object) is projected and printed on a wafer (second object) through a projection lens system. Here, before the projection exposure, an observing system (detecting means) is used to observe the reticle surface or wafer surface to detect alignment marks of the reticle and/or the wafer. On the basis of the result of detection, positional registration (alignment) between the reticle and the wafer is made.
Due to further miniaturization of semiconductor chips, improvement of precision of the relative alignment between a reticle and a wafer has been desired.
In conventional exposure apparatuses, once a reticle is aligned with respect to a reference mark provided in a portion of the exposure apparatus (reticle alignment operation), the reticle is held fixed until the next alignment operation. For this reason, the position of the reticle is dependent upon the holding performance (holding precision) of a holding member (generally, a reticle stage) for holding the reticle.
Generally, the reticle alignment is performed in response to reticle replacement. When the same reticle is used, the frequency of an alignment operation differs in dependence upon the user. If, therefore, there occurs a variation in an environment, or vibration or acceleration in the apparatus, for example, due to the influence thereof, there may occur a change in relative position between the reticle and the holding member therefor. On that occasion, when the pattern of the reticle is projected and printed on a wafer, the exposure position may displace or a deviation may occur during the exposure process. This causes degradation of resolving power for the pattern image.
It is an object of the present invention to provide an exposure apparatus by which, the position of a reticle and/or a wafer can be corrected after relative alignment of the reticle and the wafer, particularly, after alignment (reticle alignment) of the reticle with respect to a reference mark provided in a portion of the major assembly of the exposure apparatus, and by which production of large integration semiconductor devices is facilitated.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.